80 



KNOWLEDGE. 



[April 1, 1899, 



but useful organisms, the graptolites, so the trilobites have 

 been selected for the division of the Cambrian system. 

 Olenus, Pai-diliu-idcs, and Olenelhts, mark respectively the 

 Upper, Middle, and Lower Cambrian ; and the fauna 

 associated with Olendlus has naturally assumed consider- 

 able importance. 



In America, where the first forms of this trilobite were 

 described, the succession of the strata was obscured by 

 the thrusting up of the Lower Cambrian locally upon 

 higher beds, and even on the Ordovician. The fauna was 

 carefully worked out, but its importance was not at first 

 fully realised. Dr. Brogger,* however, compared it with 

 that of the Olenellus beds of Europe, which were clearly at 

 the bottom of the series ; and he urged that further 

 examination of the succession in America would lead to 

 some r€ -arrangement of ideas. Mr. Walcottf undertook 

 this work by visiting Newfoundland, where the beds were 

 less disturbed ; and in 1888 he triumphantly reported that 

 Olenellus and its associates must be placed as the funda- 

 mental fauna. Since theu the name of this trilobite has 

 become familiar, and the search for organic remains below 

 the Olenellus beds has been undertaken in every quarter 

 of the globe. 



In our own islands, inroads have been made on the 

 accepted dicta of our text-books. Prof. Lap worth J an- 

 nounced, in 1888, the discovery of Olenellus near the base 

 of the C'omley or Hollybush Sandstone in Shropshire. 

 This same Hollybush Sandstone was formerly regarded as 

 Middle Cambrian. A far more important change is the 

 consequent reference of the Longmynd mass to the Pre- 

 cambrian systems. Though its boundaries are in part 

 faulted and obscure, there is little doubt as to its antiquity, 

 especially as the aeries following upwards from the 

 Olenellus beds are represented by fossiliferous strata in the 

 same locality, quite different in character from the barren 

 slates and sandstones of the Longmynd. 



In 1891, Sir A. Geikiej recorded Olenellus from the 

 North-west Highlands of Scotland. The trilobite, and its 

 associated fauna, occur in the base of the Durness series, 

 which was long supposed to be Ordovician. This series 

 reposes unconformably on the famous Torridon Sandstone. 

 The latter thus becomes Precambrian. 



Here, then, we have in Britain two fine masses of 

 deposits in which to search for an earlier fauna than the 

 Cambrian. As yet, unfortunately, only obscure traces 

 have been discovered.,; While ripple-marks and rain- 

 prints show that the conditions of deposition resembled 

 those of modern strata near a shore, the Longmynd beds 

 for many years yielded nothing except worm-borings and 

 worm castings. Imperfect brachiopods {lAmjulce) are now 

 recorded by Prof. Blake. The Torridon Sandstone, with 

 its gritty and conglomeratic strata, is even less likely 

 to have retained traces of organisms. 



The prize may, however, ultimately fall to some unpro- 

 fessional but keen-eyed visitor to either of these interesting 

 regions. The Longmynd — the "long mountain" — forms 

 a picturesque highland, rising to seventeen hundred feet, 



* " Om alderen af Olenelluszonen," Oeol. For. Stockholm For- 

 handlUgar, Bt. YIII. (ISbS), p. 182. 



f " Succession of Cambrian faunas in N.America," Nature, Vol. 

 XXXTIII., p. 551. 



+ Geo!. Mag., 1888, p. 484 ; ibid., 1891, p. 532. 



§ Geol. May., 1891, p. 498. See also Peach and Home, Quart. 

 Jouin. Geol. Soe., Vol. XLVIII., p. 227, and Peach, ibid., Vol. L., 

 p. 661. 



II See .7. F. Blake, " Monian Eocks of Shropshire," Quart. Journ. 

 ^Geol.Soc, Yol. XLVI. (1890), p. 391; Geikie, Geol. Maa., IHdl, 

 p. 499. 



west of Church Stretton in Shropshire. Its moorland 

 slopes, cleft by steep ravines, its heather-clad crests and 

 sparkling streamlets, attract the eye by contrast with the 

 cultivated lands. Grouse still call across these wilder 

 summits ; and the geologist, cycUng, it may be, from 

 London, finds in the Longmynd his first contact with the 

 mountains. 



The Torridon Sandstone offers a far wider field. It 

 forms a sort of bulwark, a chain of fastnesses, on the north- 

 west coast of Scotland, stretching for seventy miles from 

 Loch Carron to beyond Lochinver, The total thickness is 

 estimated at from eight thousand to ten thousand feet ; 

 and Sir A. Geikie has pointed to occasional shaly bands as 

 possible preservers of the fauna. The material of the 

 sandstone is derived from the crystalline Archaean masses; 

 and in places, as on the coast of Lewis, the conglomerate 

 between the sandstone and the gneiss provides a fine 

 picture of the ancient shore. But the great secret will 

 hardly be revealed in these sandstone beds themselves. 

 Such rocks are proverbially barren ; and shells that may 

 have lain upon a pebbly beach become broken up during 

 entombment, or are dissolved away later by permeating 

 waters. The Torridon beds, moreover, may be lacustrine, 

 like the Old Red Sandstone to the east ; this would still 

 further limit their fauna, in comparison with that which 

 may be found in other areas. 



In Charnwood Forest, a rough upland rising unex- 

 pectedly through the industrial lowlands of Nottingham 

 and Leicester, another Precambrian area has been recog- 

 nised. But the slates and sandstones, associated with 

 volcanic tuffs, have here given no sign of fossils. 



In almost every region of Archfean rocks, whether we 

 select North America, Scandinavia, or Bohemia, we find 

 similar stratified Precambrian systems resting on the 

 highly metamorphosed or igneous series. These systems 

 are not likely to prove of the same geological age through- 

 out the world. If the "fundamental gneisses " represent 

 in any area the primitive crust of our cooling planet, an 

 enormous interval of time must separate the period of 

 their consolidation from that in which Olenellus flourished. 

 In the intervening deposits, the succession of which is yet 

 unknown, lies entombed the oldest fauna of the globe. 

 The earlier of these deposits must have been laid down in 

 water of high temperature ; but it is just possible that a 

 more uniform distribution of heat, and an absence of the 

 chilly depths that now prevail in our oceans, may have 

 favoured the spread of primordial life across the globe. 



Lowly forms of life, in a suitable environment, multiply 

 with extreme rapidity. Their comparative immunity from 

 disease, their simple and easily satisfied needs, the con- 

 venient interchange of their protoplasm from one individual 

 to another, give them, indeed, the semblance of immor- 

 tality. But it is only when such forms became provided 

 with a skeleton or a shell — when, in fact, their needs had 

 grown far more complex — that their remains had a chance 

 of being preserved. 



If, further, we hold with Prof. Judd* that " no good 

 reasons have been adduced for asserting that any of the 

 highly crystalline rocks — whether foliated or not — were 

 originally part of the globe as it first consolidated from a 

 state of fusion," we may well despair of finding any fauna 

 of such vast antiquity as that now under discussion. The 

 mutual interpenetration of members of the old gneissic 

 series certainly suggests that much valuable evidence has 

 been altogether swallowed up in cauldrons of re-melted 

 fundamental rocks. 



But this fascinating secret is not to be disposed of or set 



* "The Student's Lyell " (189G), p. 563. 



